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domain-specific message-handling policies for receivers, or to
request reporting of authentication and disposition of received mail.
Absent the ability to obtain feedback reports, originators who have
implemented email authentication have difficulty determining how
effective their authentication is. As a consequence, use of
authentication failures to filter mail typically does not succeed.

Over time, one-on-one relationships were established between select
senders and receivers with privately communicated means to assert
policy and receive message traffic and authentication disposition
reporting. Although these ad hoc practices have been generally
successful, they require significant manual coordination between
parties, and this model does not scale for general use on the
Internet.